Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$166.78	13.498%	$189.292	$189.29	$189.30	$189.30
Purchase #2	$137.81	9.381%	$150.738	$150.74	$150.75	$150.70
Purchase #3	$114.25	11.837%	$127.7738	$127.77	$127.75	$127.80
Purchase #4	$80.28	12.819%	$90.5711	$90.57	$90.55	$90.60
Purchase #5	$151.50	13.438%	$171.8586	$171.86	$171.85	$171.90
Purchase #6	$36.85	3.707%	$38.216	$38.22	$38.20	$38.20
Purchase #7	$203.46	7.535%	$218.7907	$218.79	$218.80	$218.80
7 purchase totals =	$890.93		$987.2402	$987.24	$987.20	$987.30